fix(tools): count AIS ship type 0 as unknown in vessel breakdowns

AIS type 0 means "not available" (ITU-R M.1371), but the source keeps it
as '0', so group_by: 'type' listed "0" as a type and understated
unknown_count. vessels_in_area rows now report it as null, and a
regression fixture mixes type 0 with Cargo and Tanker.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/tools/queries/maritime.test.mjs

@@ -225,6 +225,41 @@ test('an area search names its area to the server; a vessel lookup asks for ever
   assert.equal(lookup.has('radius_km'), false);
 });
 
+test('AIS type 0 (not available) is counted as unknown, not as a type', async () => {
+  const catalog = composeCatalog({
+    tools: coreTools,
+    services: {
+      vessels: vessels({
+        records: [
+          vessel('366000001', 37.78, -122.4, { type: '0' }),
+          vessel('366000002', 37.79, -122.41, { type: '0' }),
+          vessel('366000003', 37.77, -122.39, { type: 'Cargo' }),
+          vessel('366000004', 37.76, -122.38, { type: 'Tanker' }),
+        ],
+      }),
+    },
+  });
+  const result = await catalog.call('vessels_in_area', {
+    area: bay,
+    group_by: 'type',
+  });
+  assert.deepEqual(result.data.breakdown, {
+    field: 'type',
+    groups: [
+      { value: 'Cargo', count: 1 },
+      { value: 'Tanker', count: 1 },
+    ],
+    other_count: 0,
+    unknown_count: 2,
+  });
+  assert.match(result.summary, /most by type: Cargo \(1\), Tanker \(1\); 2 unknown\./);
+  assert.doesNotMatch(result.summary, /0 \(/);
+  assert.equal(
+    result.data.rows.find((row) => row.mmsi === '366000001').type,
+    null,
+  );
+});
+
 test('vessels in an area can be counted by destination with a speed summary', async () => {
   const catalog = composeCatalog({
     tools: coreTools,